This invention relates to the field of hydrogenation of carboxylic acids containing six or more carbon atoms and esters of such acids to form the corresponding alcohols, (i.e. alcohols which contain six or more carbon atoms). Such alcohols are valuable intermediates in the production of synthetic detergents, polymers and lubricants. More particularly, the invention relates to the regeneration of spent catalyst of the type commonly referred to as "copper chromite," when said catalyst has lost its activity in the course of being employed in the hydrogenation process.
So-called copper chromite, which is usually a mixture of cupric oxide and cupric chromite, is widely employed as a hydrogenation catalyst. Many hydrogenation process variations are employed, but one commmon embodiment comprises suspending finely-divided copper chromite in a liquid reaction mix comprising the acid, ester, alcohol or mixtures thereof, while hydrogen is passed through the suspension under conditions of elevated temperature and pressure. The copper chromite is then removed from the hydrogenation product by any suitable means, such as filtration or centrifugation, and returned to the reaction step for reuse. In the course of the hydrogenation reaction, at a rate which is dependent upon many factors including the nature of the reaction mix and the stringency of the reaction conditions being employed, a portion of the copper chromite catalyst is deactivated, with the result that it is necessary, either continuously or intermittently, to withdraw the deactivated material and replace it with fresh copper chromite.
Ordinarily the spent catalyst is either discarded or sold at a fraction of its original cost for recovery of its metal values. This results in a substantial cost to the hydrogenation process, and there has long been a recognized need for a practical method of restoring the spent catalyst to its active condition.
U.S. Pat. No. 3,699,054, Organ et al., issued Oct. 17, 1972, incorporated by reference herein, discloses a process for regenerating copper chromite catalyst, comprising the steps of:
(a) washing the catalyst in a volatile solvent (e.g., methanol) to remove organic residues from the hydrogenation reaction; PA1 (b) drying the washed catalyst to free it of the residual solvent; and PA1 (c) heating the dried catalyst in an atmosphere containing oxygen (e.g., in air) at a temperature of 100.degree. C. to 500.degree. C. for at least about 15 minutes. PA1 (1) the spent catalyst is subjected to a vacuum of 1 to 20 mm Hg at a temperature of 65.degree. C. to 320.degree. C. for a period of time sufficient to reduce the organic residue content of the spent catalyst to less than about 25% by weight; PA1 (2) the vacuum-treated catalyst from Step (1) is heated in an atmosphere comprising molecular oxygen, at a temperature of from about 260.degree. C. to 370.degree. C., whereby the remaining organic residue is burned off and the catalyst is reoxidized.
This process, when practiced on a commercial scale, suffers from the practical disadvantage of the need for handling and recovering large quantities of volatile solvents.
It is the principal object of the present invention to provide a process for regenerating the copper chromite catalyst used in hydrogenation process, without the need to use solvents.